In the area of driver assistance systems, video sensor technology is used in vehicles, among other things, for detecting traffic signs. The results of the detection are normally reconciled or combined with information from the digital map of the navigation device before being displayed to the driver. In addition to normal sheet metal traffic signs, variable message traffic signs (light signals) must also be detected, among other things. Their detection frequently presents problems due to the pulsing of the LED lamps used. The frequency of the pulsing is not perceptible to the human eye. Depending on the exposure time, the pulsing frequency of the signs and the image recording frequency of the camera, however, the “off phase” of the pulsing may also fall into the image recording period, as a result of which the sign may not be detectable completely in the image or not at all. In the most unfavorable case, this occurs over the entire period in which the sign is within the detecting range of the camera. Normally, one tries to counter this problem with appropriately long exposure times, multiple exposures or registering multiple successive images.
Patent document DE 10 2008 023 853 A1 discusses a method for detecting an object, in which at least one light source of the object illuminates in a pulsed manner and the light emitted by the light source is detectable by a detector unit and the object is detected as a function of the detection of the light, a multiple exposure being performed for detecting the light of the light source in order for the detector unit to produce an image and the entire time duration of an exposure process comprising multiple exposures being set to be greater than the time duration of an off phase of the light source during a period duration of the light of the light source that is emitted in a pulsed manner. Furthermore, a system, in particular a driver assistance system, for detecting variable message traffic signs is also described.